1. Field of the Invention
The present invention relates to an apparatus and method for performing autofocusing in an optical instrument, such as a microscope. The invention also relates to an improved microscope that includes an unfolded, main optical axis.
2. Description of the Related Art
Autofocusing techniques for microscopes have been available for many years. In a typical autofocusing technique, an objective lens is placed at a predetermined distance from the sample to be scanned, and an image is taken of the object. The image created by the microscope is then typically evaluated to determine the position at which the surface of the object, or a plane within the object, is in focus. The evaluation of the image typically involves analyzing characteristics of the image such as entropy, spatial resolution, spatial frequency, contrast, or other characteristics. The analysis of these characteristics requires a considerable amount of computer processing. Once the characteristics are analyzed, the distance between the objective lens and the object to be scanned is varied, and another image is taken. The new image is then evaluated and the process is repeated several times before a focused image is finally obtained.
Repeating the step of analyzing the image may cause the focusing operation to take an undesirably long time before the microscope is finally focused on the object surface. The need for increased processing time for autofocusing can be particularly acute for various types of imaging operations. For example, when an object is observed under a microscope, the focused conditions must be maintained in order to maintain a properly focused image of the object. Therefore, even if the object is initially in focus, the object may gradually become out of focus due to a variety of external factors such as thermal effects and vibration, if no corrective steps are taken. Moreover, when an object is larger than the field of view of the microscope, the microscope can only focus on the portion of the object that can be observed through the field of view of the microscope. Therefore, the focusing conditions must be regularly checked and adjusted In order to maintain a sharp image of the whole object.
In view of the foregoing, there is a need for an improved autofocusing system and method for a microscope that can perform quick and accurate autofocusing operations while maintaining a sharp image.